1. Field of Invention
The present invention relates to digital-to-analog converters. More particularly, the present invention relates to a digital-to-analog converter having two sections for processing an input word.
1. Description of Related Art
There are many different types of digital-to-analog converters (DAC) available, such as a resistor string (R-string) DAC. FIG. 1 illustrates a conventional R-string DAC. An R-string DAC 100 includes a resistor string of resistors 110 and a selector 120. The selector 120 includes selecting lines 124 each of which is composed of switching elements 122. Each switching element 122 is controlled by one of the bits of an input word.
The resistor string is connected between a high reference voltage (VH) and a low reference voltage (VL). Each of the selecting lines 124 is connected to one of the nodes in the resistor string. Only one of the selecting lines 124 has switches all turned on by the input word and couples the voltage on the corresponding node in the resistor string to the output node Vo.
For N-bit digital-to-analog conversion, the R-string DAC 100 requires 2N selecting lines. Moreover, each of the selected lines 124 requires N switching elements. Therefore, 2N×N switching elements are required for the N-bit R-string DAC 100. The number of switching elements dramatically increases when the bits of the input word are increased, which results in a larger layout area. This is disadvantageous for chip shrinkage and cost reduction.